Hubble constant

In summary, the conversation discusses the relationship between the speed of expansion and the radius of the Hubble sphere. It is explained that the speed of expansion is increasing, but the percentage rate of distance growth is decreasing. This is because the speed at which a distance increases can accelerate even while the percentage growth rate decreases. The conversation also touches on the idea of gravity and its potential impact on the expansion of the universe, with the conclusion that the universe is expected to continue expanding and not experience a "big crunch".
  • #1
gangula pranav
2
0
if the speed of the expansion is decreasing then it would mean that the radius of the Hubble sphere is increasing because it would require more space to expand faster than the speed of light .but as you said if the speed of expansion is increasing then why is the Hubble sphere increasing and
why is the radius of the Hubble sphere derived multiplying the speed of light with the Hubble constant where, the the Hubble constant is just the percentage of which the space is increasing while all we need to calculate the radius is the speed of expansion and not the percentage .if gravity was the answer to my previous questions then does it mean that gravity will eventualy win over and stop the expansion and start bringing things together(leading to the big crush).If so then why is that the universe is expected to turn into a cold dark and empty place?would there be a big crush or the expansion just win over and turn the universe into a vast ,cold,dark,and empty place?

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  • #2
The percentage RATE of distance growth is decreasing. A percentage growth rate is different from a speed.

The "speed of expansion" is only defined you focus on a particular distance and watch it expand over time.
If you do that, you will find that its speed of expansion is increasing and (according to standard model) will continue to increase.

The speed at which a distance increases in size can accelerate even while the percentage growth rate decreases.
and that in fact is what is actually happening.

The percentage growth RATE is settling down to 1/173 % per million years. When it has done so we will still have exponential expansion, no "crunch" expected : ^)

If you have questions about what I or others have said in some specific post, shouldn't you QUOTE the post so we can see what you are confused by?
 

What is the Hubble constant?

The Hubble constant is a measurement of the rate at which the universe is expanding. It is denoted by the symbol "H" and has units of kilometers per second per megaparsec (km/s/Mpc).

How is the Hubble constant calculated?

The Hubble constant is calculated by measuring the redshift of objects in the universe and using the Hubble-Lemaître law, which states that the farther away an object is, the faster it appears to be moving away from us. This relationship is described by the equation v = H0 x d, where v is the recessional velocity of an object, H0 is the Hubble constant, and d is the distance to the object.

Why is the Hubble constant important in cosmology?

The Hubble constant is important in cosmology because it helps us understand the age, size, and expansion rate of the universe. It is also a key parameter in determining the fate of the universe and the validity of different cosmological models.

Has the Hubble constant changed over time?

The value of the Hubble constant has been refined over time as new observational data and techniques have been developed. However, there is still debate and uncertainty about its precise value, and it is possible that it may have varied over time due to the influence of dark energy.

How does the value of the Hubble constant affect our understanding of the universe?

The value of the Hubble constant is crucial in determining the expansion rate of the universe and therefore its age and size. It also has implications for understanding the distribution of matter and energy in the universe and the overall structure and evolution of the cosmos.

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